FIG. 1 shows a prior art railway switch 10. The switch 10 includes fixed rails 22a and 24a secured to railroad ties 26. The switch layout 10 also includes switching rails 22b and 24b positioned inside the fixed rails 22a, 24a. An actuator 28 is provided for moving the switching rails 22b, 24b between a first position (shown in FIG. 1) and a second position (not shown). In the first position, the switching rail 22b contacts the fixed rail 22a and the switching rail 24b is offset from the fixed rail 24a. In the second position, the switching rail 22b is offset from the fixed rail 22a, and the switching rail 24b contacts the fixed rail 24a. The actuator 28 is linked to the switching rails 22b, 24b by a throw rod 30.
In northern climates, snow and ice can accumulate at the switch 10 and thereby interfere with the movement of the switching rails 22b, 24b between the first and second positions. To prevent the accumulation of snow and ice, a hot air blower 32 is provided for melting snow and ice at the switch 10. A duct assembly 34 carries hot air from the blower 32 to the switch 10. The duct assembly 34 includes a lateral duct 36, a tie duct 38, inner track ducts 40 and outer track ducts 42 (only one shown). The lateral duct 36 extends from the blower 32 to the tie duct 38. The tie duct 38 extends beneath the fixed rails 22a, 24a, and supports the rails 22a, 24a. The inner track ducts 40 extend generally perpendicularly outwardly from the tie duct 38. The inner track ducts 40 are positioned inside the switching rails 22b, 24b and are generally parallel to the switching rails 22b, 24b. The outer track ducts 42 also extend perpendicularly outwardly from the tie duct 38. The outer track ducts 42 are positioned outside the fixed rails 22a, 24a and are generally parallel to the fixed rails 22a, 24a. The track ducts 40, 42 are connected to the tie duct 38 by track duct nozzles 44. The track ducts 40, 42 include punch-outs (not shown) where holes can be formed for directing hot air from the track ducts 40, 42 toward selected locations of the switch 10. The duct assembly 34 can also include point nozzles 46 coupled to the tie duct 38. The point nozzles 46 function to direct hot air at the contact points between the fixed rails 22a, 24a and the switching rails 22b, 24b. 
FIGS. 2 and 3 show the tie duct 38 in more detail. Generally, the tie duct 38 is a railroad tie-shaped duct constructed of a material such as metal. The tie duct 38 has a hollow, generally rectangular cross-section and has end flanges 48 for coupling either end of the tie duct 38 to the lateral duct 36. As depicted in FIGS. 2 and 3, the ends of the tie duct 38 are enclosed by end plates 39. When the tie duct 38 is installed at a railway site, at least one of the end plates 39 is removed prior to attaching the lateral duct 36 to the corresponding end flange 48 of the tie duct 38 so that fluid communication is provided between the interior of the lateral duct 36 and the interior of the tie duct 38.
Referring still to FIGS. 2 and 3, the fixed rails 22a, 24b are secured to the tie duct 38 by a conventional rail fastening arrangement. For example, as shown at FIGS. 2 and 3, the fixed rails 22a, 24a are secured to the tie duct 38 by tie plates 50 fastened to the top side of the tie duct 38, and e-clips 52 that link the tie plates 50 to the fixed rails 22a, 24a so that the rails are fixed to the top sides of the tie plates 50.
The top side of the tie duct 38 also defines openings for providing fluid communication between the hollow interior of the tie duct 38 and the inner track ducts 40, the outer track ducts 42, and the point nozzles 46. For example, openings 54 in the tie duct 38 provide fluid communication with the outer track ducts 42, openings 56 in the tie duct 38 provide fluid communication with the inner track ducts 40, and openings 58 in the tie duct 38 provide fluid communication with the point nozzles 46. When the track ducts 40, 42 or the point nozzles 46 are not installed on the tie duct 38, cover plates 60 (shown mounted over the openings 54) can be mounted over the openings 54, 56 or 58 to prevent debris from entering the interior of the tie duct 38.
Referring to FIGS. 4-6, the point nozzles 46 are fastened to the top wall of the tie duct 38 at locations over the openings 58. Preferably, the point nozzles 46 are fastened to the tie duct 38 by a fastening arrangement that electrically isolates the point nozzles 46 from the tie duct 38. As shown at FIGS. 4 and 5, the fastening arrangement includes bolts 62 that extend through curved openings 64 defined by a bottom flange 66 of the point nozzle 46. The bolts 62 are typically threaded within tapped openings 63 defined through a top wall 65 of the tie duct 38. A screen 68 is mounted at the top side of the tie duct 38. The screen 68 covers the opening 58 to prevent animals (e.g., rodents) or debris from entering the interior of the tie duct 38. A dielectric gasket 70 is mounted between the screen 68 and the bottom flange 66. The gasket 70 has a shape that generally matches the shape of the bottom flange 66 and functions to electrically isolate the flange 66 from the top side of the tie duct 38. The bolts 62 are also preferably electrically isolated from the point nozzle 46. As shown at FIG. 4, a dielectric bushing/spacer 72 isolates the shank of the bolt 62 from the bottom flange 66, and a dielectric washer 74 electrically isolates the head of the bolt 62 from the point nozzle 46. The fastening assembly also includes a flat washer 76 positioned below the dielectric washer 74, a flat washer 78 positioned above the dielectric washer 74, and a split lock washer 80 positioned between the flat washer 76 and the head of the bolt 62. It will be appreciated that four of the bolt fastening assemblies are provided for each of the point nozzles 46.
Fastening arrangements are also used to fasten the track duct nozzles 44 to the top wall of the tie duct 38. The track duct nozzles 44 corresponding to the inner track ducts 40 are mounted over the openings 56, and the track duct nozzles 44 corresponding to the outer track ducts 42 are mounted over the openings 54. Similar to the point nozzles 46, it is desirable for the track duct nozzles 44 to be electrically isolated from the tie duct 38.
Referring to FIGS. 7-9, an example fastening arrangement for securing the track duct nozzles 44 to the top wall 65 of the tie duct 38 is shown. The fastening arrangement includes a plurality of bolts 82 that are mounted through openings 84 defined through a bottom flange 86 of the track duct nozzle 44. Typically, the bolts 82 are threaded within tapped openings 67 defined through the top wall 65 of the tie duct 38. A dielectric gasket 90 having a shape that generally matches the shape of the bottom flange 86 is mounted beneath the bottom flange 86. The gasket 90 functions to electrically insulate the bottom flange 86 from the top side of the tie duct 38. A screen 88 is mounted between the gasket 90 and the top side of the tie duct 38. The screen 88 prevents animals or debris from entering the interior of the tie duct 38. The bolts 82 are also preferably electrically isolated from their corresponding track duct nozzles 44. For example, as shown at FIG. 7, a dielectric spacer/bushing 92 and a dielectric washer 94 are provided for each bolt 82. The dielectric spacers/bushings 92 isolate the shanks of the bolts 82 from the bottom flange 86, and the dielectric washers 94 electrically isolate the heads of the bolts 82 from the bottom flanges 86. The fastening assemblies also include a flat washer 98 positioned above each dielectric washer 94, and a split lock washer 100 positioned between each flat washer 98 and the head of each corresponding bolt 82. Adhesive 101 can be used to provide a seal at the interface between the track duct nozzles 44 and the track ducts 40 and 42.